Your emails have not been sent out and you receive a bounce saying You have reached a limit for sending mail. This article explains what happened, and why.
Why have my emails not been sent out?
When you complete a mail merge, you might notice that some of your emails have not been sent.
YAMM specifies it in your spreadsheet with the 'EMAIL_NOT_SENT' mention, under the 'Merge status' column:
This happens because we failed to calculate properly your remaining quota. For some reasons, YAMM detected that you had fewer quota than it actually was.
Google blocked my account after receiving the bounces. What happened?
In an effort to fight spam, prevent abuse and unusual activity, Google will temporarily disable your account if you send messages to more than 500 recipients or if you send a large number of undeliverable messages.
To avoid this situation, please respect the general rules about emailing to avoid spam issues described in this following article 'Tips: How to avoid being blocked by Google or spam filters'
We invite you to consult this documentation for more information: 'My account has been blocked by Google'